VICKY McClure had told herself she must not cry, she should not cry. After all, unlike members of the titular choir the Line of Duty actor was putting together, she did not have dementia. 

Certainly, her beloved nana had suffered with it, and that was how she came to lead this two-part documentary, but tears? Not from her, not on this watch. 

In the event, and with more than a few bitten lips along the way, she made it almost to the end before she could hold back no longer. Well done DCI Fleming: that was much further than most who saw this deeply moving piece of television.

McClure’s film set out to show the positive effects singing and music have on the brain, and find out what relevance this might have in treating dementia. The hope is if scientists can understand how music “lights up” the brain, literally, as we could see from MRI scans, they might be closer to finding a way of stopping it shutting down.

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The science was important, but this was a human interest story first and foremost, a small but vital glimpse into the lives of some of the 850,000 people with dementia in the UK. People such as Julie, 50, whose three daughters worry about her constantly; Chris, 67, whose devoted wife spoke of dementia as something “we” have; and Betty, 82, married for 64 years. “Never a crossed word, I’ve got a big blister on my tongue,” she joked. 

Then the one that turned McClure into a puddle of tears: Daniel, 31, who inherited a rare form of early onset Alzheimer’s. Daniel is the dad of two-year-old twins. He was diagnosed after their first birthday. There is a 50-50 chance the children will have the gene; they can find out, if they wish, when they are 18. “So bloody cruel,” said McClure. Given it was after the watershed, one would have forgiven her for being more explicit. 

Daniel and the rest of the volunteers were put through their paces by choirmaster Mark De-Lisser. Helping him were some of the singers who had performed Stand By Me at Harry and Meghan’s wedding. Class acts all round, and none more so than McClure. 

She was the perfect host, warm and comforting as tea and toast, funny, modest, and oh so natural with people. She went for a brain scan to see what music did to her brain. “The most reassuring thing is that you are going to see that there is one in there,” the consultant told her. Everyone’s a comedian. 

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There were some genuinely amusing moments, with people able to laugh about some of the effects of this dreadful disease. One husband couldn’t help himself saying risque things, totally out of character with the person he was, much to his wife’s good-natured exasperation. 

Despite the subject matter, this was a film that soared with joy. It showed the cruelty of the condition, but also the patience and love of the carers. As they watched their loved ones sing, the people they thought had been lost forever returned to their old selves. Just for a moment, but what a moment. 

Next week, McClure and her fellow singers continue working their way towards a performance at the Royal Concert Hall in Nottingham, her hometown, in front of 2,000 people. In the meantime, McClure’s headline gig will be the Line of Duty finale on Sunday, about which there are already acres of speculation in the press. 

Whatever happens in Jed Mercurio’s drama, we can say one thing with absolute certainty about the final part of Our Dementia Choir: there won’t be a dry eye in the house.